STATE  OF  ILLINOIS 

STATE  HIGHWAY  DEPARTMENT 


BULLETIN  NO.  6 

ON; 

Dust  Prevention 


Including  Specifications  for  Oils  and  Tars  Used  in 
Surface  Treatment  of  Various  Types  of  Roads. 


Prepared  By 


FRANK  L.  ROMAN, 

Testing  Engineer,  Illinois  Highway  Department. 


Springfield,  Illinois,  March,  1915. 


ILLINOIS  STATE  GEOLOGICAL  SURVEY 


3 305 


00010  2586 


STATE  OF  ILLINOIS. 

STATE  HIGHWAY  DEPARTMENT. 


BULLETIN  NO.  6. 

ON 

Dust  Prevention 


BY 

F.  L.  ROMAN,  Testing  Engineer. 
Illinois  Highway  Department. 


COMMISSION. 

A.  D.  Gash,  President. 

S.  E.  Bradt,  Secretary. 

James  P.  Wilson. 

Wm.  W.  Marr,  Chief  State  Highway  Engineer. 

P.  C.  McArdle,  Assistant  State  Highway  Engincci 
Clifford  Older,  Bridge  Engineer. 

H.  E.  Bilger,  Road  Engineer. 

F.  L.  Roman,  Testing  Engineer. 


Springfield,  Illinois. 
March,  1915. 


Schnefp  & Barnes,  State  Printers 
Springfield,  III. 

1915 


CONTENTS, 


pAge. 

Introduction  7 

Dust  Formation 7 

Dust  Prevention.... 9 

Dust  on  Pavements ! 11 

Dust  Prevention  on  Concrete  and  Brick  Roads 11 

Asphalts  and  Tars  on  Concrete  and  Brick  Roads 12 

Dust  on  Creosoted  Block  Pavements 12 

Dust  on  Bituminous  Pavements 12 

The  Repairing  and  Surfacing  of  Bituminous  Roads... 13 

Specifications  No.  1 (for  the  Purchase  of  a Heavy  Oil  Suitable  for  the 

Surface  Treatment  of  Bituminous  or  Waterbound  Macadam) 16 

Specifications  No.  2 (for  the  Purchase  of  a Medium  Oil  Suitable  for  the 

Surface  Treatment  of  Bituminous  or  Waterbound  Macadam) 16 

Specifications  No.  3,  (for  the  Purchase  of  a Refined  Coal  Tar  Product 
Suitable  for  the  Surface  Treatment  of  Bituminous  or  Waterbound 

Macadam)  17 

Dust  on  Macadam  Roads 17 

Specifications  No.  4 (for  the  Purchase  of  a Light  Oil  Suitable  for  the  Sur- 
face Treatment  of  Macadam  or  Gravel  Roads) 25 

Specifications  No.  5 (for  the  Purchase  of  a Tar  Product  Suitable  for  the 

Surface  Treatment  of  Macadam  or  Gravel  Roads).. 25 

Dust  on  Gravel  Roads .- 27 

Dust  on  Earth  Roads 30 

Oiling  of  Earth  Roads 33 

Specifications  No.  6 (for  the  Purchase  of  a Light  Oil  Suitable  for  the 

Surface  Treatment  of  Earth  Roads) 35 

Miscellaneous  Bituminous  Materials 36 

Oil  and  Tar  Emulsions 37 

Calcium  Chloride 38 

Miscellaneous  .Materials 39 

Glutrin  39 

Sodium  Silicate 39 

Suitability  of  Materials 40 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/dustpreventionOOroma 


PREFACE. 


The  State  Highway  Department  has  in  the  past  year  received 
numerous  requests  for  information  pertaining  to  dust  prevention 
in  general,  and  to  surface  oiling  of  macadam,  gravel  and  dirt  roads 
in  particular.  The  following  treatise  has  been  prepared  in  an 
attempt  to  compile  in  readily  available  form,  data  and  suggestions 
which  would  answer  these  inquiries  in  many  instances,  and  which 
would  educate  the  public  to  the  various  ways  of  eliminating  dust. 
It  is  not  intended  to  cover  in  detail  all  that  might  be  said  in  regard 
to  dust  prevention,  but  rather  to  give  a general  outline  of  the  sub- 
ject, together  with  suggestions  as  to  practical  methods  to  eliminate 
dust.  An  effort  has  been  made  to  write  this  bulletin,  as  far  as 
possible,  in  plain,  non-technical  language  and  to  deal  with  the 
subject  in  such  a way  as  to  be  helpful  to  township,  county  and  city 
officials  who  are  required  to  cope  with  the  dust  problem. 


INTRODUCTION. 


The  formation  of  dust  on  roads  and  its  prevention  by  various 
means  has  given  rise  to  serious  problems.  While  the  dust  nuisance 
has  been  a source  of  annoyance  for  a number  of  years,  little  atten- 
tion has  been  given  to  the  means  of  preventing  dust  until  recent 
years.'  With  rapid  increase  in  population  and  traffic,  and  the 
advent  of  motor-driven  vehicles,  the  formation  of  road  dust  in 
excessive  quantity  has  become  a public  menace  as  well  as  a public 
nuisance.  Dust  carries  filth  and  disease  germs,  and  is  an  import- 
ant cause  of  disease  to  mankind  and  animals ; it  is  unsightly  on 
trees,  shrubbery  and  plants,  and  when  deposited  in  large  quantities, 
is  disastrous  to  vegetation ; it  is  not  only  a source  of  annoyance  to 
traffic  by  soiling  clothes  and  vehicles,  but  is  a danger  when  form- 
ing clouds  which  obstruct  the  traveled  way  and  conceal  the  pres- 
ence of  fast  moving  vehicles ; it  is  a perpetual  nuisance  to  residents 
along  highways,  by  damaging  clothing  and  household  furnishings 
and  causing  much  personal  discomfort. 

DUST  FORMATION. 

The  fundamental  cause  of  dust  formation  on  roads  is  wear. 
Other  factors,  such  as  the  transportation  and  deposition  on  the 


Figure  1.  The  Scraping  on  the  Highways  of  the  Sod  and  Debris  from  the  Ditches  is  Often  the 
Cause  of  the  Bad  Condition  of  the  Road. 

road  of  foreign  material,  should  also  be  taken  into  consideration, 
but  the  dust  due  to  the  last  cause  is,  however,  generally  of  small 
importance  compared  to  that  due  to  wear. 


8 


Broadly  speaking,  wear  on  a road  surface  consists  of  the  break- 
ing up  of  the  solid  road  surface  into  fine  particles,  or  dust.  This 
action  takes  place  under  the  various  forces  due  to  traffic  mainly, 
such  as  the  grinding  of  the  steel  tired  wheels,  the  blows  of  horses’ 
hoofs,  the  local  compression  of  narrow  tires  from  vehicles  heavily 
loaded,  the  frictional  effect  of  motor-driven  vehicles,  etc.  Some 
action  is  due  also  to  frost,  rain,  wind  and  other  weathering  agencies 
which  tend  to  disintegrate  the  road  surface. 

Foreign  materials  carried  on  the  road  by  traffic  may  be  depos- 
ited already  as  dust  or  may  be  converted  into  dust  by  the  same 
wearing  agencies  which  have  been  described  above.  The  dust 
from  this  source  is  of  special  importance,  mainly  in  thickly  settled 
districts  where  the  dust  on  roads  is  sometimes  due  almost  entirely 
to  foreign  matter. 

Wind  and  traffic  raise  the  dust  formed  from  wear  or  other 
agencies,  and  the  discomforts  resulting  are  too  well  known  to 


Figure  2.  The  Highways  Are  Often  Considered  as  Dumping  Grounds  for  All  Sorts  of  Refuse. 

The  Placing  of  Rubbish  on  Highways  or  in  the  Side  Ditches  Should  Not  Be  Permitted. 

require  further  discussion.  This  dust  nuisance  has  been  greatly 
increased,  however,  by  the  use  of  fast  moving  motor  vehicles. 
The  partial  vacuum  and  suction  which  are  produced  behind  the 
body  of  an  automobile  draw  the  dust  into  the  air  and  the  air  currents 
resulting  from  the  passage  of  high  speed  vehicles  scatter  the  dust 
over  the  surrounding  country.  The  higher  the  speed  of  the  machine, 
the  larger  will  be  the  amount  of  dust  raised. 

The  effect  of  automobiles  on  certain  types  of  roads  is  well 
known.  On  stone  and  gravel  roads,  the  friction  of  the  wheels  of 
motor  driven  vehicles,  and  the  suction  of  these  vehicles  when 
driven  at  high  speed,  remove  the  fine  particles  which  are  necessary 
to  bind  the  stones,  and  the  road  is  torn  up  in  a short  time.  These 
conditions  of  stone  and  gravel  roads  are  not  general,  however,  in 
this  State,  as  there  are  many  sections  in  Illinois  where  motor 


9 


traffic  is  yet  very  light,  but  they  have  been  discussed  to  show  the 
necessity  of  providing  for  new  conditions  of  traffic. 

It  should  be  noted  in  regard  to  automobile  traffic,  that  while 
motor  vehicles  have  undoubtedly  caused  much  trouble  on  certain 
types  of  road,  that  many  types  of  pavements  withstand  automobiles 
much  better  than  horse-drawn  vehicles.  If  the  dust  problem  alone 
is  considered,  it  should  be  remembered  also  that  the  dust  nuisance 
existed  on  a somewhat  smaller  scale  long  before  the  first  automobile 
was  constructed,  and  that  if  self-pro!pelled  vehicles  have  tem- 
porarily increased  the  dust  nuisance,  they  have  also  aroused  the 
public  at  large  to  the  knowledge  that  good  roads  are.  necessary  to 
the  welfare  of  any  community.  Bad  roads  are  as  injurious  to  the 
automobile  as  self-propelled  vehicles  are  to  some  types  of  road,  and 
consequently  the  automobile  has  been  instrumental  in  the  construc- 
tion of  many  miles  of  good  roads.  A large  portion  of  the  money 
spent  on  the  roads  of  Illinois  during  the  past  two  years  has  been 


Figure  3.  Dust  Raised  by  Automobile  Going  80  Miles  an  Hour. 


furnished  by  automobile  taxation,  and  automobile  clubs  have  in 
various  ways  cooperated  in  building  good  roads.  The  coming  of 
the  automobile  has  done  much  towards  revolutionizing  our  trans- 
portation facilities  and  increasing  the  religious,  educational  and 
industrial  welfare  of  the  community,  and  the  above  discussion  on 
automobile  traffic  has  been  written  in  an  effort  to  dispel  the  feeling 
still  retained  by  a few,  that  automobiles  are  a nuisance  on  high- 
ways and  that  modern  road  legislation  is  of  benefit  only  to  auto- 
mobilists. 

DUST  PREVENTION. 

Many  methods  to  eliminate  the  dust  nuisance  on  roads  have 
been  tried,  but  the  dust  problem  may  be  solved  only  in  three  general 
ways : first,  by  the  sanitary  removal  of  the  dust ; second,  by  the 


10 


construction  of  roads  which  will  not  form  dust ; and  third,  by  the 
retention  of  the  dust  formed  on  the  road  surface. 

The  first  of  these  methods  applies  mainly  to  city  pavements 


N. 


Figure  4.  An  Old  Macadam  Road  in  Bad  Condition. 


and  requires  either  sweeping  the  streets  or  washing  them  with 
water  under  pressure.  It  is  impracticable  on  country  highways  and 
will  not  be  given  further  consideration  in  this  publication. 


Figure  5.  The  Same  Road  as  Shown  in  Figure  4 After  Improvement. 


The  methods  of  dust  prevention,  involving  either  the  construc- 
tion of  roads  which  will  not  form  dust,  or  the  retention  of  the 
dust  formed  on  the  road  surface  are  closely  related  and  will  be 
discussed  together,  in  connection  with  the  various  types  of  roads. 


11 


DUST  ON  PAVEMENTS 

Pavements  are  generally  understood  to  mean  brick,  concrete, 
creosoted  block,  asphalt,  tar  and  similar  types  of  roads.  They  are 
the  most  resistant  to  wear  and  form  very  little  dust  when  properly 
constructed.  The  dust  accumulating  on  these  roads  is  due  almost 
entirely  to  foreign  matter  carried  on  the  road  by  traffic.  A dis- 
cussion of  the  methods  of  construction  of  pavements  is  beyond  the 
scope  of  this  bulletin  and  will  not  be  undertaken.*' 

Road  preservation  and  dust  prevention  are,  however,  so  closely 
associated  in  certain  types  of  roads  that  it  will  be  necessary  to  consider 
the  repairing  of  some  types  of  pavements  in  connection  with  dust  pre- 
vention. 


DUST  PREVENTION  ON  CONCRETE  AND  BRICK  ROADS. 

As  stated  before,  concrete  and  brick  roads  form  very  little  dust. 
In  cities,  however,  a large  amount  of  dust  from  foreign  materials 
often  accumulates  on  these  pavements  and  it  is  necessary  to  resort 


Figure  6.  Showing  End  of  Brick  Pavement  and  the  Bad  Conditions  of  an  Earth  Road  from  Which 
Mud  Is  Carried  onto  Pavement  by  Traffic. 


to  sweeping  or  washing  at  frequent  intervals.  As  this  causes  a 
heavy  expense,  solutions  of  calcium  chloride  and  other  dust  pal- 
liatives have  been  applied  with  some  success  to  these  pavements 
to  retain  the  dust  on  the  road  surface.  Their  effect  in  cities,  is 
at  best  only  temporary,  but  as  the  dust  does  not  have  to  be  removed 
so  frequently,  the  saving  effected  may  more  than  offset  the  extra 
cost  of  these  treatments.  Applications  of  calcium  chloride  and 


* For  methods  of  construction  see  the  specifications  of  the  Illinois  Highway  Department  for 
various  types  of  pavements.  Copies  of  the  following  specifications  may  be  obtained  free  of 
charge : Brick  Road  Construction ; Concrete  Road  Construction ; Waterbound  Macadam  Con- 
struction ; Bituminous  Macadam  Construction,  comprising  asphalt  or  tar  road  construction. 


12 


similar  products  are  especially  effective  in  the  suburbs  of  large 
cities  where  the  removal  of  dust  is  very  difficult  and  expensive. 
Brick  and  concrete  roads  on  rural  highways  show,  in  general,  very 
little  dust,  and  the  rains  are  usually  sufficient  to  wash  off  the  dust 
and  impurities  deposited  by  traffic. 

ASPHALTS  AND  TARS  ON  CONCRETE  AND  BRICK 
, ROADS. 

The  application  of  asphalts  and  tars  on  concrete  and  brick 
roads  has  been  tried  repeatedly  in  many  cities.  These  experiments 
have  been,  in  general,  a waste  of  time  and  money,  and  have  been 
at  best  only  temporarily  successful.  While  it  is  undoubtedly  true 
that  the  application  of  a bituminous  surface  on  concrete  or  brick 
will  render  these  pavements  practically  noiseless  and  will  tend  to 
retain  the  dust  to  some  extent,  it  has  been  found  difficult  to  build 
a mat  of  this  type  which  will  not  peel  or  “pick  up”  in  patches. 
The  accumulation  of  foreign  matter  on  the  road  has  furthermore  a 
destructive  influence  on  the  thin  bituminous  mats  used,  and  bitu- 
minous surfaces  less  than  y2  inch  in  thickness  soon  wear  out. 

DUST  ON  CREOSOTED  BLOCK  PAVEMENTS. 

Creosoted  block  pavements  form  practically  no  dust  and  when 
new  tend  to  lay  the  dust  which  is  brought  on  their  surface  by 
traffic.  These  blocks  are  treated  with  creosote  oils  under  pressure, 
and  contain  generally  from  10  to  20  pounds  of  the  oil  per  cubic 
foot  of  lumber.  During  warm  weather,  when  the  dust  nuisance 
is  greatest,  a small  amount  of  oil  is  generally  forced  out  of  the 
blocks  through  expansion.  This  oil  will  have  the  tendency  to 
lay  the  dust,  and  if  the  foreign  material  deposited  on  the  pavement 
is  removed  before  it  has  accumulated  to  a great  thickness,  the  road 
will  remain  practically  dustless.  These  creosoted  block  pavements 
lose  somewhat  their  property  of  laying  dust  when  old,  but  when 
the  dust  question  alone  is  considered,  they  compare  favorably  with 
concrete  and  brick  pavements  and  often  with  bituminous  surfaces. 
Up  to  the  present  time  creosoted  blocks  have  not  been  used  on  rural 
roads  in  this  State,  but  have  been  used  mainly  in  cities,  and  to  some 
extent  in  the  suburbs  of  large  cities. 

DUST  ON  BITUMINOUS  PAVEMENTS. 

The  bituminous  pavements  include  asphalt,  tar  and  similar  types 
of  roads,  but  in  the  following  discussion  they  are  not  understood 
to  mean  various  types  of  pavements  to  which  a light  mat  or  carpet 
of  bituminous  material  has  been  applied.  A large  number  of  bit- 
uminous pavements  have  been  built  within  the  last  five  years,  and 
the  popularity  of  this  type  of  pavement  is  due  to  a large  extent 
to  the  fact  that  it  remains  practically  dustless  under  ordinary 
conditions.  In  cities,  where  a large  amount  of  foreign  material 
is  deposited  on  these  pavements,  they  should  be  cleaned  at  fre- 
quent intervals,  not  only  to  assist  them  in  keeping  a dustless  sur- 


13 


face,  but  because  the  dust  and  especially  the  dung  of  animals  is 
injurious  to  this  type  of  construction.  On  rural  highways  the 
amount-  of  dust  carried  on  the  road  is  usually  comparatively  small 
and  the  rains  are  sufficient  to  wash  the  bituminous  surface  free  of 
foreign  deposits.  Where  short  sections  of  bituminous  roads  have 
been  built,  large  quantities  of  mud  are  often  carried  on  these  pave- 
ments from  the  adjacent  earth  roads  and  should  be  removed.  The 


Figure  7.  A Bituminous  Macadam  Road  Four  Years  Old  in  Very  Good  Condition.  The  Leaves 
and  Debris  Should  Be  Removed  from  the  Gutters. 


use  of  a light  road  grader  or  drag  to  clean  the  surface  by  scraping 
off  the  mud  has  been  suggested,  but  is  not  always  practicable. 
The  building  of  a few  yards  of  stone  or  gravel  roads  at  each  end 
and  on  the  cross  roads  would  usually  prevent,  to  some  extent,  this 
occurence. 

THE  REPAIRING  AND  SURFACING  OF  BITUMINOUS 

ROADS. 

The  mat  surface  of  bituminous  roads  wears  off  slowly  and  after 
a certain  length  of  time,  depending  on  the  amount  of  traffic  carried 
by  the  road  and  various  other  conditions,  will  be  worn  through, 
and  the  stone  will  be  required  to  sustain  the  main  part  of  the  wear 
due  to  traffic.  With  the  soft  limestones  commonly  used  in  Illinois, 
the  road  will  no  longer  remain  dustless  and  will  deteriorate  rapidly. 
The  careful  inspection  of  many  bituminous  macadam  roads  of  this 
State  has  always  shown  that  a mat  surface  into  which  has  been 
incorporated  a hard  silicious  material  will  wear  much  better  than 
the  body  of  the  road,  and  that  it  is  therefore,  advisable  to  apply 
Occasionally  a new  carpet  of  bituminous  material  to  take  the  wear. 

The  bituminous  material  used  for  this  surface  treatment  should 
be  applied  only  after  the  road  has  been  swept  clean  and  after  all 
irregularities  of  the  surface  have  been  eliminated  by  proper  repairs. 
All  depressions  should  be  filled  with  bituminous  material  and 


14 


gravel  or  stone  chips,  so  that  the  entire  road  surface  is  hard  and 
even.  The  application  of  the  bituminous  material  may  be  made 
either  by  hand  or  by  mechanical  methods.  In  the  hand  method, 
ordinary  pouring  cans  are  used  and  filled  from  a large  supply  tank 
that  is  driven  along  beside  the  work.  It  is  very  difficult  to  apply 
the  bituminous  material  evenly  with  a pouring  can,  and  it  is  neces- 
sary to  immediately  follow  the  application  with  a brush  broom 
and  sweep  the  surplus  oil  ahead.  This  method  of  applying  the 
material  is  very  slow  and  expensive  and  is  seldom  used  today, 
except  for  small  jobs  and  patch  work. 

There  are  a great  many  different  types  of  mechanical  distrib- 
utors on  the  market,  and  a number  will  apply  equally  well  light 
or  heavy  bituminous  materials.  The  apparatus  which  is  used  by 
the  Illinois  Highway  Department  is  described  in  connection  with 
the  construction  of  bituminous  surfaces  on  waterbound  macadam 


Figure  8.  A Bituminous  Macadam  Road  in  a Very  Bad  Condition.  The  Road  Should  Be  Patched 
and  Resurfaced.  The  Condition  of  the  Road  Appears  to  Be  Due  Partly  to  Improper  Construc- 
tion and  Partly  to  Lack  of  Maintenance. 


roads.  The  bituminous  material  is  applied  at  the  rate  of  about  J4 
gallon  per  square  yard  and  should  be  covered  with  only  the  quan- 
tity of  clean  coarse  sand  which  will  be  required  to  prevent  it  from 
adhering  to  wheels.  When  hot  bituminous  materials  are  used,  the 
application  of  sand  should  follow  at  once.  On  heavily  traveled 
roads,  much  better  results  can  be  secured  by  applying  the  bitumin- 
ous surface  in  two  courses.  ' The  first  treatment  should  consist  of 
about  34  gallon  of  material  per  square  yard  and  should  be  covered 
with  torpedo  gravel  of  % to  *4  inch  size,  or,  if  gravel  is  not  available, 
with  clean  stone  chips.  After  rolling,  a second  treatment  of  about 
34  gallon  of  bituminous  material  per  square  yard  is  applied.  Cle'an 
coarse  sand  is  spread  over  the  surface  and  the  road  rolled  a second 
time.  The  entire  treatment  will  require  from  y2  to  £4  gallon  of 
bituminous  material  per  square  yard,  and  one  cubic  yard  of  coarse 
sand  or  chips  for  about  every  125  square  yards  of  surface  treated. 


15 


The  resulting  mat  should  be  about  y$  inch  thick,  and  the  more 
uniform  the  thickness  is  the  better  will  be  the  results  obtained. 
A one  course  treatment  with  the  lighter  oils  given  under  specifica- 
tions No.  2,  should  require  from  ^ to  ^ gallon  of  oil  and  one 
cubic  yard  of  sand,  for  every  150  square  yards  of  surface. 

Asphalts  and  tars  may  be  lised  for  bituminous  roads  and  for 
surface  treatments  with  about  equal  success.  A good  asphaltic 
oil  would  be  preferred  to  a tar  of  poor  quality,  but  a tar  of  good 
quality  would  be  preferred  to  a greasy  paraffin  asphalt.  It  is 
not  advisable,  however,  to  use  a tar  product  on  an  asphalt  road, 
nor  an  asphalt  on  a tar  road,  and  a bituminous  road  should  be 
repaired  and  re-surfaced  with  a material  of  the  same  nature  as  that 
used  in  its  construction.  The  following  specifications  are  given 
as  a guide  for  the  selection  of  the  best  grades  of  asphaltic  oils  and 


Figure  9.  Hoad  Showing  Surface  Bituminous  Mat  Worn  off  in  Spots  and  Requiring  a Surface 
Application  of  a Good  Bituminous  Material. 


coal  tar  products  suitable  for  the  surface  treatment  of  bituminous 
roads.  The  price  of  the  bituminous  products  meeting  the  require- 
ments of  the  following  specifications  varies  from  about  6 cents  to 
16  cents  per  gallon,  and  the  cost  per  square  yard  of  this  surface 
construction  will  vary  from  about  6 cents  to  20  cents,  depending 
upon  the  quality  and  quantity  of  the  oil  used  and  local  conditions. 
Specifications  No.  1 are  to  be  used  for  heavy  asphaltic  oils  which 
are  very  viscous  and  sticky  at  ordinary  temperatures,  and  which 
must  be  heated  before  application.  Specifications  No.  2 are  in- 
tended for  asphaltic  or  semi-asphaltic  oils  of  medium  weight  which 
can  be  applied  cold,  when  the  air  temperature  is  at  least  80  degrees 
F.  Specifications  No.  3 are  to  be  used  for  refined  coal  tar  products 
which  are  viscous  at  ordinary  temperature  and  should  be  applied 
hot.  Lighter  bituminous  materials  are  not  recommended  for  this 
type  of  construction,  but  if  desired,  may  be  obtained  by  requiring 
products  meeting  specifications  Nos.  4 or  5. 


16 


SPECIFICATIONS  NO.  1. 

HEAVY  OIL  FOR  SURFACE  TREATMENT  OF  BITUMINOUS  OR  WATERBOUND 

MACADAM. 

(Hot  Application.) 

1.  The  oil  shall  be  a very  viscous  fluid  product,  free  from  water. 

2.  Specific  Gravity.  Its  specific  gravity  at  25°  C.  (77°  F.)  shall 
not  be  less  than  0.980. 

3.  Total  Bitumen.  It  shall  be  soluble  in  chemically  pure  cold 
carbon  disulphide  to  the  extent  of  at  least  99.5  per  cent. 

4.  Naphtha  Insoluble  Bitumen.  Of  the  total  bitumen  not  less 
than  10  nor  more  than  25  per  cent  shall  be  insoluble  in  86°  B.  paraffin 
naphtha,  at  air  temperature. 

5.  Fixed  Carbon.  The  fixed  carbon  shall  not  be  less  than  5.0 
nor  more  than  13.0  per  cent. 

6.  Penetration.  The  penetration  of  the  material  as  determined 
with  a Dow  machine,  using  a No.  2 needle,  100  grams  weight,  5 
seconds  time  and  a temperature  of  25°  C.  (77°  F.)  shall  not  be 
less  than  25.  mm. 

7.  Viscosity.  When  240  cc.  of  the  oil  are  heated  in  an  Engler 
Viscosimeter  to  100°  C.  (212°' F.)  and  maintained  at  this  temperature 
for  3 minutes,  the  first  50  cc.  which  flow  through  the  aperture  shall 
show  a specific  viscosity  of  not  less  than  five  (5.0).  In  this  test  special 
care  should  be  taken  to  prevent  any  appreciable  loss  through  volatil- 
ization. 

8.  Loss  on  Evaporation.  When  20  grams  of  the  oil  (in  a tin 

dish,  2J4  inches  in  diameter  and  Y inch  deep  with  vertical  sides)  are 

maintained  at  a temperature  of  163°  C.  (325°  F.)  for  5 hours  in  a N.  Y. 
Testing  Laboratory  oven,  the  loss  shall  not  exceed  15  per  cent  by 
weight. 

9.  Flash  Point.  The  flash  point  of  the  oil  by  the  open  cup  method 
should  not  be  less  than  100°  C.  (212°  F.) 

SPECIFICATIONS  NO.  2. 

MEDIUM  OIL  FOR  SURFACE  TREATMENT  OF  BITUMINOUS  OR  WATERBOUND 

MACADAM. 

(Should  Be  Applied  Hot  When  Air  Temperature  Is  Below  80°  F.) 

1.  The  oil  shall  be  a viscous  fluid  product,  free  from  water. 

2.  Specific  Gravity.  Its  specific  gravity  at  25°  C.  (77°  F.) 

shall  not  be  less  than  0.950. 

3.  Total  Bitumen.  It  shall  be  soluble  in  chemically  pure  cold 
carbon  disulphide  to  the  extent  of  at  least  99.5  per  cent. 

4.  Naphtha  Insoluble  Bitumen.  Of  the  total  bitumen,  not  less 
than  5 nor  more  than  20  per  cent  shall  be  insoluble  in  86°  B.  paraffin 
naphtha  at  air  temperature. 

5.  Fixed  Carbon.  The  fixed  carbon  shall  not  be  less  than  4.0 
nor  more  than  12.0  per  cent. 


17 


6.  Viscosity.  When  240  cc.  of  the  oil  are  heated  in  an  Engler 
Viscosimeter  to  50°  C.  (122°  F.)  and  maintained  at  this  tem- 
perature for  5 minutes,  the  first  50  cc.  which  flow  through  the  aper- 
ture shall  show  a specific  viscosity  of  not  less  than  thirty  (30)  nor 
more  than  seventy  (70). 

7.  Loss  on  Evaporation.  .When  20  grams  of  the  oil  (in  a tin 
dish  2 inches  in  diameter  and  24  inch  deep  with  vertical  sides)  are 
maintained  at  a temperature  of  163°  C.  (325°  F.)  for  5 hours  in  a N.  Y. 
Testing  Laboratory  oven,  the  loss  shall  not  exceed  25  per  cent  by 
weight. 

8.  Flash  Point.  The  flash  point  of  the  oil  by  the  open  cup 
method  should  not  be  less  than  100°  C.  (212°  F.) 

SPECIFICATIONS  NO.  3. 

REFINED  COAL  TAR  PRODUCTS  FOR  SURFACE  TREATMENT  OF  BITUMINOUS 
OR  WATERBOUND  MACADAM. 

(Hot  Application.) 

1.  The  tar  shall  be  free  from  water  and  shall  not  foam  when 
heated  to  110°  C.  (230°  F.) 

2.  Specific  Gravity.  Its  specific  gravity  at  25°  C.  (77°  F.) 
shall  not  be  less  than  1.18  nor  more  than  1.24. 

3.  Inorganic  Matter.  It  shall  not  show  more  than  0.5  per  cent 
of  ash  upon  ignition. 

4.  Free  Carbon.  Its  free  carbon  content  shall  not  be  less  than 
12.0  nor  more  than  22.0  per  cent.  In  determining  the  free  carbon, 
the  coal  tar  product  will  be  dissolved  in  chemically  pure  cold  carbon 
disulphide  and  the  residue  filtered  on  a Gooch  crucible.  The  per 
cent  residue  minus  the  per  cent  of  ash  will  be  taken  as  the  per  cent  of 
free  carbon.  No  centrifuge  shall  be  used  in  this  test. 

5.  Consistency.  The  consistency  of  the  tar  as  determined  by  the 
Howard  and  Morse  float  apparatus  at  a temperature  of  32°  C.  (90°  F.) 
shall  not  be  less  than  iy2  nor  more  than  2^4  minutes. 

6.  Distillation.  Fractional  distillation  by  the  method  described 

in  bulletin  No.  38  of  the  U.  S.  Office  of  Public  Roads  shall  give 

results  conforming  to  the  follownig  requirements,  all  measurements 

being  by  weight: 

Up  to  110°  C.  the  distillate  shall  not  exceed  1 per  cent. 

Up  to  170°  C.  the  distillate  shall  not  exceed  8 per  cent. 

The  total  distillate  up  to  315°  C.  shall  be  at  least  20  per  cent. 

DUST  ON  MACADAM  ROADS. 

On  this  type  of  construction,  dust  prevention  is  closely  related 
to  road  preservation.  A large  portion  of  the  dust  is  due  to  wear 
of  the  road  itself,  and  the  ability  of  the  macadam  road  to  form 
dust  is  therefore  to  some  extent  a measure  of  its  wear. 

It  is  estimated  that  about  50  per  cent  of  the  existing  hard  roads 
in  Illinois  have  been  constructed  of  crushed  stone,  and  that  the 
same  material  will  be  used  for  about  30  per  cent  of  the  hard  roads 


18 


to  be  built  during  the  next  5 years.  While  it  is  realized  that  under 
certain  conditions  there  is  a heavy  maintenance  expense  connected 
with  the  use  of  these  roads,  yet  their  low  initial  cost  makes  them 
very  popular.  There  are  many  sections  in  this  State  that  have  little 
or  no  hard  surfaced  roads,  and  as  the  popular  desire  is  to  secure 
large  mileage  under  any  hard  road  improvement  plan,  macadam 
or  gravel  roads  are  favored. 

The  methods  used  in  the  construction  of  macadam  roads  vary 
a great  deal,  and  the  amount  of  dust  on  the  roads  will  depend  upon 
the  method,  and  also  upon  the  quality  of  the  stone  used  in  their 
construction. 

It  will,  therefore,  be  necessary  to  consider  some  phases  of  the 
construction  and  repair  of  these  roads  in  connection  with  dust 
prevention. 

A well  built  waterbound  macadam  road  will  be  practically 
dustless  and  remain  in  good  condition  for  a number  of  years,  while 
a road  built  by  simply  dumping  crushed  limestone  upon  the  high- 
way, may  be  dusty  from  the  start,  and  if  not  maintained  properly 
will  soon  grind  up  and  disintegrate.  Even  where  the  best  methods 


Figure  10.  Macadam  Hoad  Built  without  the  Use  of  a Boiler.  The  Light  Drag  Can  Be  Used 
Effectively  on  This  Type  of  Road. 


of  construction  have  been  used,  proper  care,  including  dragging, 
patching  and  surfacing  may  be  required  from  the  beginning  to 
obtain  the  best  results.  Most  of  the  macadam  roads  in  Illinois 
are  built  of  rather  soft  limestone  which  will  deteriorate  rapidly, 
and  it  is  urged  that  a definite  plan  of  maintenance  be  put  into 
operation  as  soon  as  practicable,  and  before  the  -repair  work 
becomes  unduly  expensive. 

The  light  road  drag  may  be  used  effectively  in  maintaining 
macadam  roads  which  have  been  built  without  the  use  of  a roller. 
The  dragging  will  fill  all  wheel  ruts  and  depressions,  and  help  in 
maintaining  the  desired  crown.  The  loose  stones  are  brought  back 


19 


into  place,  and  on  roads  which  have  been  swept  by  automobile 
traffic,  much  of  the  old  bonding  material  can  be  restored  to  the 
road  surface  if  the  drag  is  used  at  the  proper  time. 

Rut  formation  is  of  great  importance  in  relation  to  both  dust 
formation  and  road  preservation,  and  steps  should  be  taken  to 
prevent  rutting,  as  far  as  possible,  and  to  repair  all  ruts  and  depres- 
sions before  the  road  starts  to  disintegrate.  Rutting  may  be  pre- 
vented to  a great  extent  by  the  construction  of  wide  roads  with  a 
minimum  crown  and  a hard  smooth  surface  that  is  as  suitable  for 
driving  in  one  place  as  in  another.  When  ruts  or  depressions  are 
formed  which  cannot  be  readily  filled  by  the  road  drag,  they  should 
be  filled  with  limestone  and  screenings.  In  this  patching  work,  it 
is  often  necessary  to  make  the  sides  of  the  depressions  vertical  by 


Figure  11.  Macadam  Road  Showing  Need  of  Repairs  by  Patching. 


means  of  a scarifier  or  a hand  pick,  and  it  is  practically  impossible 
to  fill  shallow  depressions  properly,  if  this  precaution  has  not  been 
taken.  The  depression  is  filled  with  coarse  stone  and  thoroughly 
compacted  into  place  by  means  of  a hand  tamper  or  a roller.  The 
surface  is  then  covered  with  limestone  screenings  and  thoroughly 
soaked  with  water  to  wash  fine  materials  into  the  voids  of  the 
stone  and  assist  in  bonding. 

A road  that  is  patched  promptly  with  a suitable  material  will 
have  the  original  surface  restored,  and  the  necessity  of  a surface 
dressing  or  a complete  reconstruction  will  often  be  eliminated.  If 
the  macadam  road  has  not  received  proper  maintenance,  or  is  sub- 
jected to  heavy  traffic,  it  may  require,  however,  a new  wearing  or 
bonding  surface.  Heavy  automobile  traffic,  especially,  will  soon 
sweep  off  the  surface  of  a macadam  road  all  bonding  material  and 
require  surface  treatment  of  some  kind,  either  limestone  screen- 
ings or  bituminous  material.  Roads  in  this  condition  present  a 
mosaic  surface,  and  if  they  are  not  given  proper  attention  the  traffic 


20 


will  soon  loosen  some  of  the  stones  and  the  road  will  ravel  rapidly. 
A light  dressing  of  good  bonding  limestone  screenings  as  soon  as 
indications  of  raveling  appear,  will  often,  however,  prevent  the 
destruction  of  the  road.  This  surface  dressing  is  applied  primarily 
to  supply  bonding  material  and  should  be  applied  as  often  as 
required,  but  never  to  a depth  greater  than  an  inch.  An  excess  of 
screening  does  not  help  in  bonding,  and  will  grind  up  to  form 
dust.  It  is  a waste  of  money  and  only  a cause  of  dust  nuisance. 
The  screenings  should  be  spread  evenly  over  the  road  and  then 
saturated  thoroughly  with  water  to  help  them  in  bonding  to  the  old 
surface. 


Figure  12.  A Well  Constructed  Macadam  Road,  Four  Years  Old,  Resurfaced  with  2 Inches  of 
Coarse  Stone,  Improperly  Bonded.  Money  and  Material  Practically  Wasted. 


Under  heavy  automobile  traffic,  a surface  dressing  of  limestone 
screenings  is  at  best  only  temporary*  Much  better  results  may  be 
obtained  from  the  standpoint  of  dust  prevention  as  well  as  road 
preservation,  by  the  application  of  an  oil  or  tar  product.  The 
bituminous  material  is  applied  in  a manner  similar  to  the  method 
described  in  the  surface  treatment  of  bituminous  roads.  Care 
should  be  taken,  however,  that  the  surface  has  been  previously 
swept  entirely  clean  of  dust  and  foreign  materials,  and  that  the 
stones  are  well  exposed.  Ordinary  street  sweepers  or  hand  brooms 
may  be  used,  but  sweeping  with  hand  brooms  will  prove  slow  and 
expensive.  All  depressions  in  the  road  are  then  filled  with  clean 
gravel  or  chips  and  bituminous  material,  and  the  oil  or  tar  is 
applied  only  after  the  road  is  entirely  clean  and  uniformly  hard. 
The  character  of  the  road  obtained  and  its  ability  to  resist  the 
wear  due  to  traffic,  will  depend  to  a large  extent  upon  the  bond 
between  the  bituminous  mat  and  the  stone  of  the  old  road.  If 
properly  built,  a surface  will  be  obtained  which  can  compare  fav- 


21 


orably  with  that  of  a bituminous  macadam,  and  some  of  the  best 
bituminous  road  surfaces  in  this  State  have  been  obtained  by  this 
type  of  construction. 


Figure  13.  Showing  Effect  of  Automobile  on  a Macadam  Road. 

As  wearing  qualities  of  a bituminous  surface  are  largely 
increased  by  greater  uniformity  in  the  thickness  of  the  mat,  mechan- 
ical distributors  are  now  almost  exclusively  employed  in  this  work. 


Figure  14.  A Macadam  Road  Swept  Free  of  Its  Bonding  Material  by  Heavy  Automobile  Traffic. 
An  Application  of  Good  Bituminous  Material  Would  Be  the  Most  Satisfactory  Method  of 

Maintaining  This  Road 

The  apparatus  which  is  used  by  the  Illinois  Highway  Department 
has  been  designed  so  that  it  will  apply  either  light  or  heavy  bitu- 
minous materials,  and  in  any  desired  quantity.  The  apparatus  is 


22 


composed  of  a steel  tank  of  600  gallons  capacity,  mounted  on  a heavy 
truck  and  provided  with  necessary  attachments  for  heating  and  distri- 
bution. The  steel  tank  is  air  tight  and  is  designed  to  withstand 
an  internal  pressure  of  100  pounds  per  square  inch.  A furnace 
which  will  burn  either  wood  or  coal  is  at  the  rear  end  of  the  dis- 
tributor, while  a Westinghouse  air  pump  is  attached  to  its  front 
end  and  is  connected  with  the  steam  roller  so  that  pressure  or 
vacuum  can  be  secured  in  the  tank  very  quickly.  A guage  is  placed 
at  the  top  of  the  distributor  for  pressure  readings  and  a thermo- 
meter is  attached  at  the  rear  end  to  indicate  the  temperature  of 
the  binder. 

The  bituminous  material  is  conducted  from  the  tank  to  the 
spray  by  a flexible  metal  hose  which  can  be  carried  by  one  rpan, 
and  permits  the  operator  to  apply  either  large  or  small  quantities 
as  desired.  Attached  to  the  end  of  the  metal  hose  is  a spraying 
nozzle  as  shown  in  figure  17. 

Steam  is  conducted  from  the  roller  to  the  nozzle  by  a inch 
pipe,  and  the  arrangement  of  the  apparatus  is  such  that  the  bitu- 
minous material  is  forced  through  the  iy2  inch  hose  and  pipe,  and 
as  it  is  discharged  from  the  nozzle,  a jet  of  steam  blows  into  the 
binder  breaking  it  into  a fine  spray.  In  this  manner,  the  bitu- 


Figure  15.  Applying  Bituminous  Material  with  Hand-pouring  Cans.  This  Method  of  Application 
Is  Slow  and  Expensive,  Put  May  Be  Most  Satisfactory  for  Repair  Work  and  Small  Jobs. 


minous  material  may  be  applied  uniformly  over  the  surface  of  the 
road. 

This  apparatus  has  proven  to  be  very  satisfactory  as  it  will 
apply  any  grade  of  binder,  and  in  any  quantity  desired.  The  force 
with  which  the  binder  leaves  the  nozzle  aids  it  in  pentrating  all 
interstices  in  the  road,  as  well  as  freeing  the  stones  of  any  dust 
coating.  The  practice  a few  years  ago  was  to  deliver  the  bitu- 
minous material  in  railroad  tank  cars  to  a convenient  siding  where 


23 


the  material  was  heated  and  pumped  directly  into  the  distributing 
wagon  and  hauled  to  the  road.  This  system  may  be  used  to 
advantage  with  fluid  road  oils,  but  with  the  heavier  products,  the 
expense  connected  with  heating  the  railroad  tank  cars  and  the 
difficulty  of  having  sufficient  road  surface  prepared  to  received  at 
one  time  8,000  to  10,000  gallons  of  bituminous  material,  makes  this 
system  very  impractical. 

It  is  much  more  convenient  to  have  the  heavy  bind-ers  delivered 
on  the  road  in  barrels  or  metal  drums.  These  barrels  or  drums  are 
emptied  in  auxiliary  kettles  having  a capacity  of  about  450  gallons 
and  which  may  be  filled  and  heated  while  the  pressure  tank  is  being 
emptied. 

The  bituminous  material  is  applied  at  the  rate  of  l/z  to  ^4 
gallons  per  square  yard,  either  in  one  or  two  treatments,  and  one 
cubic  yard  of  gravel  or  screenings  is  used  for  every  100  to  150 
square  yards  of  road  surface.  The  price  of  the  oils  or  tars  used 


Figure  16.  Applying  Hot  Bituminous  Material  by  Means  of  Air  Pressure  and  Steam  Spray 

Combined . 

in  .this  surface  treatment  will  vary  from  4 to  16  cents  per  gallon, 
depending  upon  the  grade  of  the  material.  A number  of  products 
of  good,  quality  may  be  obtained  for  about  8 cents  per  gallon, 
making  the  cost  of  construction  6 to  15  cents  per  square  yard, 
depending  upon  local  conditions.  It  is  recommended  that  in  choos- 
ing the  grade  of  oil  to  be  used,  careful  consideration  be  given  to 
the  condition  of  the  road  and  to  the  amount  of  traffic  upon  it.  In 
surfacing  a road  which  has  started  to  ravel  and  where  most  of  the 
stone  has  been  swept  bare  of  all  fine  bonding  material,  a bitumi- 
nous product  meeting  the  requirements  of  specificatiqns  No.  1 or 
No.  3 should  be  used.  An  oil  obtained  under  specifications  No.  2 
should  be  used  on  a macadam  road  when  more  fine  material  remains 
and  the  large  stones  are  not  so  apparent;  while  a product  meeting 


24 


the  requirements  of  specifications  No.  4 or  5 would  give  the  best 
results  on  a road  with  a closed  hard  bound  surface  difficult  to  sweep 
clean  of  dust  and  fine  material. 


The  bituminous  products  purchased  under  specifications  Nos. 
4 or  5,  may  be  applied  cold,  but  a tar  product  meeting  specifica- 
tions No.  5 will  tend  to  track  under  traffic,  and  in  most  cases,  is 
not  recommended. 


Figure  17.  Details  of  Nozzle  for  Spraying  Bituminous  Materials.  Used  by  the  Illinois  Highway  Department. 


25 


SPECIFICATIONS  NO.  4. 

LIGHT  OIL  FOR  SURFACE  TREATMENT  OF  MACADAM  OR  GRAVEL  ROADS. 

(Cold  Application.) 

1.  The  oil  shall  be  a fluid  product,  .free  from  water. 

2.  Specific  Gravity.  Its  specific  gravity  at  25°  C.  (77°  F.)  shall 
not  be  less  than  0.930. 

3.  Total  Bitumen.  It  shall  be  soluble  in  chemically  pure  cold 
carbon  disulphide  to  the  extent  of  at  least  99.5  per  cent. 

4.  Naphtha  Insoluble  Bitumen.  Of  the  total  bitumen,  not  less 
than  4.0  nor  more  than  15.0  per  cent  shall  be  insoluble  in  86°  B.  paraf- 
fin naphtha,  at  air  temperature. 

5.  Fixed  Carbon.  The  fixed  carbon  shall  not  be  less  than  3.0 
per  cent. 

6.  Viscosity.  When  240  cc.  of  the  oil  are  heated  in  an  Engler 
Viscosimeter  to  50°  C.  (122°  F.)  and  maintained  at  this  temperature 
for  5 minutes,  the  first  50  cc.  which  flow  through  the  aperture  shall 
show  a specific  viscosity  of  not  less  than  15  nor  more  than  30. 

7.  Loss  on  Evaporation.  When  20  grams  of  the  oil  (in  a tin 
dish  21/,  inches  in  diameter  and  ^4  inch  deep  with  vertical  sides)  are 
maintained  at  a temperature  of  163°  C.  (325°  F.)  for  5 hours  in 
a N.  Y.  Testing  Laboratory  oven,  the  loss  shall  not  exceed  25  per  cent 
by  weight. 


SPECIFICATIONS  NO.  5. 

TAR  PRODUCT  FOR  SURFACE  TREATMENT  OF  MACADAM  OR  GRAVEL  ROADS. 

(Cold  Application.) 

1.  The  tar  shall  be  free  from  water. 

2.  Specific  Gravity.  Its  specific  gravity  at  25°  C.  (77°  F.)  shall 
not  be  less  than  1.12  nor  more  than  1.22. 

3.  Inorganic  Matter.  It  shall  show  not  more  than  0.5  per  cent 
of  ash  upon  ignition. 

4.  Free  Carbon.  Its  free  carbon  content  shall  not  be  more  than 
20  per  cent. 

5.  Viscosity.  When  240  cc.  of  the  tar  product  are  heated  in  an 
Engler  Viscosimeter  to  50°  C.  (122°  F.)  and  maintained  at  this  tem- 
perature for  5 minutes,  the  first  50  cc.  which  flow  through  the  aper- 
ture shall  show  a specific  viscosity  of  not  less  than  20  nor  more  than 
40. 

6.  Distillation.  Fractional  distillation  by  the  method  described 

in  bulletin  No.  38  of  the  U.  S.  Office  of  Public  Roads  shall  give 

results  conforming  to  the  following  requirements,  all  measurements 

being  by  weight : 

Up  to  110°  C.  the  distillate  shall  not  exceed  2 per  cent. 

Up  to  170°  C.  the  distillate  shall  not  exceed  10  per  cent. 

The  total  distillate  up  to  315°  C.  shall  not  be  less  than  25 
per  cent  nor  more  than  45  per  cent. 


26 


When  macadam  roads  have  become  so  badly  worn  that  it  is 
impossible  to  keep  them  in  good  condition  by  ordinary  methods 
of  maintenance,  a partial  reconstruction  of  the  road  becomes  nec- 
essary. This  is  often  done  by  simply  dumping  a few  inches  of 
stone  on  the  road  and  spreading  it  more  or  less  evenly.  As  much 
more  stone  is  required  in  the  depressions  of  the  old  road  than  on 
the  high  places,  the  thickness  of  the  new  material  will  vary  widely 
and  will  not  compact  uniformly  under  traffic.  This  will  cause  the 
road  to  wear  unevenly  again  and  ruts  and  depressions  will  soon 
be  formed.  By  far,  better  results  may  be  obtained  by  first  loosen- 
ing the  surface  of  the  old  road,  either  by  spiking  or  by  scarifying. 
Some  roads  may  then  be  harrowed,-  shaped  and  rolled  without 
adding  any  new  material.  The  usual  method  of  repairing  is, 
however,  to  add  before  rolling  about  3 inches  of  stone,  to  harrow 
a second  time  and  roll.  Screenings  are  then  added  and  the  road  is 
thoroughly  soaked  with  water  to  assist  in  binding  the  surface. 


Figure  18.  Bituminous  Macadam  Road  Resurfaced  with  Heavy  Asphaltic  Oil. 


The  cost  of  loosening  the  old  road  with  spikes  in  the  roller 
wheels  is  about  1J4  to  2 cents  per  square  yard,  and  with  a scarifier 
from  y2  to  1 cent  per  square  yard.  The  average  total  cost  of  resur- 
facing macadam  roads  by  the  method  described  is  about  10  cents 
per  square  yard  for  each  inch  of  new  material  added. 

In  the  partial  reconstruction  of  macadam  roads,  it  is  often 
advantageous  to  build  a bituminous  macadam  instead  of  a new 
waterbound  surface.  The  method  of  construction  is  similar  to 
that  of  the  waterbound  macadam  just  described,  up  to  the  time 
the  stone  is  in  place  and  has  been  rolled.  Just  enough  clean  chips 
are  then  added  to  fill  the  larger  voids  in  the  stone  and  a first  coat 
of  hot  bituminous  material  is  applied.  Clean  chips  are  brushed 
into  the  remaining  voids  of  the  surface,  and  the  road  smoothed  with 
a roller.  A seal  coat  of  bituminous  material  is  then  applied  and 
coarse  sand  or  chips  are  spread  again  over  the  surface  and  the  road 


87 


rolled  lightly.  If  necessary,  more  sand  or  chips  are  added  so  as 
to  prevent  tracking  of  the  surface  under  traffic.  It  is  essential  in 
this  work  that  the  stone  and  chips  should  be  clean,  and  with  dusty 
stone,  good  use  should  be  made  of  the  harrow  to  take  the  dust 
and  fine  material  to  the  bottom  before  rolling  the  stone.  The  suc- 
cess of  this  construction  depends  largely  upon  the  ability  of  the 
binder  to  adhere  or  stick  to  the  stones.  The  surface  should  be 
firm,  and  pockets  of  dust  or  fine  material  should  be  carefully 
avoided.  The  bituminous  material  does  not  penetrate  through  dust 
and  fine  material,  and  the  mat  applied  on  a pocket  of  this  kind  is 
likely  to  pick  up  under  traffic.  It  should  be  noted  also,  that  as  the 
bituminous  material  excludes  the  presence  of  moisture,  a dust 
pocket  will  be  unable  to  bind  as  it  does  in  waterbound  macadam, 
and  will,  therefore,  always  remain  a weak  spot  on  the  road  surface. 

The  amount  of  binder  used  will  depend  to  some  extent  upon 
the  amount  of  new  stone  added  to  the  road.  With  3 inches  of  new 


Figure  19.  Macadam  Road  Partly  Reconstructed  with  Heavy  Asphaltic  Oil. 


stone,  from  1 to  ll/2  gallons  of  binder  should  be  used  for  the  first 
application  and  one-third  to  one-half  gallon  for  the  second  applica- 
tion or  seal  coat.  The  most  satisfactory  binder  for  this  type  of 
construction  is  a heavy  material,  either  tar  or  asphalt,  such  as  the 
bituminous  products  used  in  the  construction  of  bituminous  ma- 
cadam by  the  penetration  method.  Further  information  as  to  the 
requirements  of  these  products  may  be  obtained  by  requesting  a 
copy  of  “Specifications  for  Bituminous  Macadam  Construction,” 
from  the  Illinois  Highway  Department,  Springfield,  111. 

DUST  ON  GRAVEL  ROADS. 

This  type  of  road  may  be  considered  as  a go-between  or  com- 
promise between  macadam  and  the  earth  road.  While  some  gravel 
roads  show  a hard,  well  bound  surface,  others  are  found  which  are 


28 


dusty  and  little  better  than  earth  roads.  A large  variety  of  ma- 
terials are  used  in  their  construction,  due  mainly  to  local  conditions, 
but  often  also  to  a misunderstanding  of  the  quality  of  gravels 


Figure  20.  A Gravel  Road  Needing  Better  Drainage  and  Repairs. 


required.  Gravels  containing  a large  per  cent  of  hard  coarse  peb- 
bles, from  three  inches  to  one-half  inch  in  size,  and  from  ten  to 
twenty  per  cent  of  red  clay  with  good  binding  qualities,  such  as 


Figure  21.  A Gravel  Road  in  Bad  Condition  and  Which  Should  Be  Reconstructed. 


are  found  in  the  extreme  southern  counties  of  the  State,  will  give 
roads  which  often  compare  favorably  with  waterbound  macadam. 
These  roads  are  somewhat  dusty  at  first,  but  the  excess  of  clay  will 


29 


soon  work  out  under  traffic  and  leav-e  a hard  smooth  surface.  The 
maintenance  of  such  a road  is  very  similar  to  that  of  a crushed 
stone  road,  a good  bonding  gravel  being  used  for  patching  and 
surfacing  in  place  of  stone  and  screening. 


Figure  22.  Dusty  Condition  of  a Gravel  Road  After  a Dry  Season. 


1 Many  of  the  materials  used  consist  mainly  of  fine  sand  and 
clay  or  of  soft  materials  which  grind  up  readily  under  traffic.  The 
resulting  roads  are  very  dusty  in  dry  weather  and  muddy  in  rainy 


Figure  23.  A Well  Built  Gravel  Road,  Oiled  and  Practically  Dustless. 


weather,  and  do  not  deserve  the  name  of  hard  roads.  The  dust  can 
be  materially  reduced,  however,  by  frequent  dragging  and  elim- 
ination of  the  ruts.  This  dragging  is  also  of  special  benefit  to 


30 


gravel  roads  built  of  clean  gravels  which  lack  binder  and  tend  to 
keep  rolling  under  traffic.  The  drag  will  bring  any  loose  pebbles 
back  into  the  depressions,  and  enough  earth  will  usually  be  carried 
on  the  gravel  to  assist  in  bonding  the  surface.  Care  should  be 
taken,  however,  against  scraping  an  excess  of  earth  to  the  center 
of  the  road,  as  this  will  only  increase  dust  formation. 

It  is  seldom  that  a gravel  road  can  be  constructed  with  a sur- 
face so  hard  and  clean  that  it  will  permit  the  successful  application 
of  a heavy  oil  or  tar.  An  oil  which  would  meet  specifications  No.  2 
might  be  used  on  a clean  gravel  road,  while  materials  meeting 
specifications  No.  4 and  No.  5 would  be  more  satisfactory  for  the 
surface  treatment  of  the  average  gravel  road.  The  lighter  oils  of 
specifications  No.  6,  oil  emulsions,  calcium  chloride  and  miscel- 
laneous dust  palliatives  can  also  be  used  on  these  roads  for  tem- 
porary dust  prevention. 

DUST  ON  EARTH  ROADS. 

The  dust  nuisance  and  the  mud  problem  on  earth  roads  in 
Illinois  have  become  proverbial  and  need  no  introduction.  In  late 
winter  and  early  spring,  when  the  thawing  out  of  the  ground  has 
taken  place,  some  of  these  roads  become  impassable  morasses,  while 


Figure  24.  Proper  Drainage  and  Occasional  Dragging  Would  Prevent  the  Condition  Shown  in  This 
Illustration.  These  Muddy  Roads  Are  also  the  Ones  on  Which  the  Dust  Nuisance  Is  the 
Worst  after  a Dry  Season. 


in  summer  from  4 to  6 inches  of  dust  are  sometimes  found  on  these 
roads  and  a fast-moving  automobile  will  raise  so  much  dust  that 
one  wonders  “where  it  all  comes  from.” 

The  number  of  hard  roads,  including  many  gravel  roads  of 
poor  quality,  is  relatively  small,  and  for  many  years  yet  to  come 


31 


the  earth  roads  will  represent  at  least  80  per  cent  of  the  roads  in 
the  State.  The  improvement  of  these  roads,  to  make  them  at  least 
passable  at  all  seasons,  is  therefore  of  special  interest.  While  the 


Figure  25.  A Well  Built  Earth  Road.  The  Center  Is  Maintained  with  the  Drag. 


character  of  an  earth  road  cannot  be  changed  entirely  without  a 
large  expenditure,  yet  it  may  be  ameliorated  to  a large  extent  at 
small  cost. 


Figure  26.  This  Condition  of  an  Earth  Road  Was  Found  During  September.  It  Shows  Utter 
Lack  of  Any  Intelligent  Care.  A Few  Loads  of  Earth  to  Raise  the  Road  Here  Would 
Prevent  Any  Such  Mud  Hole  in  Summer  Time,  at  Least. 


The  two  most  important  factors  in  the  proper  maintenance  of 
this  type  of  road  are  drainage  and  dragging.  It  has  been  assumed 
during  the  previous  discussion  of  the  hard  types  of  roads,  that  the 


32 


first  step  in  their  construction  had  been  to  secure  good  drainage. 
The  earth  road,  however,  often  lacks  proper  drainage  entirely.  A 
few  drains  under  the  low  spots  and  good  open  wide  ditches  will  do 


Figure  27.  The  Road  Drag  at  Work.  Note  the  Angle  It  Makes  with  the  Road,  so  That  a Small 
Amount  of  Material  Is  Pushed  to  the  Center  of  the  Road. 


Figure  28.  This  Form  of  a Drag  Suitable  for  Very  Sticky  Soils.  Here  the  Drag  Is  Used  Mainly 
as  a Slicker.  If  It  Is  Turned  Over,  the  Edge  of  the  Plank  Acts  as  a Cutter  to  Move  a Small 
Amount  of  Material. 


much  towards  preventing  the  formation  of  morasses  and  will  tend 
to  make  the  road  dry  rapidly.  The  drainage  will  be  further  assisted 
by  the  use  of  the  road  drag  to  smooth  the  surface  of  the  road  and 
prevent  the  formation  of  depressions. 


33 


Dragging  is  considered  of  such  importance  that  an  educational 
campaign  on  this  subject  was  started  several  years  ago  in  Illinois. 


Figure  29.  Effect  of  Slicker  on  Black,  Gumbo  Soil.  Such  Soil  Cannot  Be  Dragged  Successfully 
Until  Partially  Dried  so  as  not  to  Roll  or  Stick  to  the  Drag. 

A special  bulletin  has  been  prepared  by  the  State  Highway 
Department  on  the  construction  of  the  road  drag  and  its  use,  and 
may  be  obtained  free  of  charge  upon  request. 

OILING  OF  EARTH  ROADS. 

Of  late  years  much  attention  has  been  given  to  the  surface 
oiling  of  these  earth  roads.  In  the  late  spring  of  each  year  the 
State  Highway  Department  receives  a large  number  of  requests 
for  information  upon  this  subject.  Many  grades  of  oils  have  been 
used  under  various  conditions,  and  there  seems  to  be  a great  deal 
of  misunderstanding  as  to  the  qualities  which  the  oil  should  pos- 
sess, and  the  conditions  under  which  it  should  be  applied. 

In  general,  the  road  oils  used  during  the  past  year  were  too 
light.  These  light  paraffin  oils  have  practically  no  binding  value 
and  leave  only  a greasy  residue.  They  have  given  trouble  on  many 
occasions,  and  in  some  cases  have  been  a nuisance  worse  than  the 
dust.  A good  illustration  of  the  troubles  arising  from  the  use  of  a 
poor  grade  of  oil  is  given  in  the  following  extract  from  a letter 
received  by  the  State  -Highway  Department  during  the  summer  of 
1914  from  a township  commissioner  of  highways: 

“In  oiling  our  streets  we  were  unfortunate  enough  to 
place  our  order  for  oil  with  an  old  and  apparently  reliable 
house,  giving  us  a 40  per  cent  asphalt  guarantee,  but  which 
has  proven  unsatisfactory,  there  not  being  enough  binder  in  it, 
and  our  streets  have  worked  up  a loose  oily  dust  from  one  to 
three  inches  thick,  covering  the  whole  width  of  the  streets. 
This  is  beginning  to  be  light  enough  to  fly  in  the  air,  and  still 


34 


has  enough  oil  in  it  to  prevent  settling  by  rain.  It  is  a bad 
situation,  but  what  can  we  do  with  it?  I take  it,  it  would  not 
do  to  oil  on  it,  unless  a very  heavy  oil  would  cement  it  enough 
to  iron  out  solid.  We  dislike  to  scrape  it  into  the  gutter  and 
stop  our  drainage,  and  cannot  afford  to  haul  it  off.  Can  you 
advise  the  best  way  to  proceed  under  the  circumstances  ?” 
Light  semi-asphaltic  oils  with  a base  having  good  binding 
qualities  have  on  the  contrary  given  good  results,  especially  if 
applied  under  proper  conditions.  It  has  been  found  that  even  with 
-the  best  grades  of  road  oils,  it  is  alzvays  advisable  to  oil  the  dry  road 
after  the  dust  has  been  well  settled , either  by  rain  or  sprinkling. 


Figure  30.  An  Oiled  Earth  Road. 


Proper  oiling  of  an  earth  road  in  spring  will  prevent  the  dust 
nuisance  during  the  summer  and  will  leave  the  road  in  better  condition 
generally.  The^use  of  these  oils  is  primarily  to  lay  the  dust  tempo- 
rarily, but  the  application  of  an  oil  of  good  quality  will  often  improve 
the  road  to  some  extent  for  a long  length  of  time.  The  selection  of  a 
suitable  grade  of  oil  should,  however,  be  given  a great  deal  more  con- 
sideration than  it  has  received  in  many  of  the  small  towns  in  Illinois 
in  the  past  years.  The  belief  that  any  cheap  grade  of  oil  is  good 
enough  to  lay  the  dust  is  entirely  erroneous.  Furthermore,  the  appli- 
cation of  some  of  these  greasy  paraffin  oils  has  caused  the  formation 
in  rainy  weather  of  a slippery  mud  worse  for  traffic  than  the  dust  in 
dry  weather. 

During  1914,  a number  of  requests  to  test  road  oils  which  had 
been  bought  under  a “40  per  cent  asphaltum  guarantee”  were  received, 
and  it  seems  necessary  to  issue  a warning  against  purchasing  oils 
under  guarantees  of  this  kind  which  are  worthless.  Correspondence 
with  township  commissioners  has  generally  brought  out  the  informa- 
tion that  the  oils  were  purchased  under  this  guarantee  in  the  belief 
that  the  oil  should  leave  40  per  cent  of  “asphalt  residue,”  and  not 


35 


realizing  that  the  residues  obtained  on  evaporation  might  be  entirely 
different  in  character,  nor  that  varying  percentages  of  residue  might 
be  obtained,  depending  upon  the  consistency  to  which  the  oil  was 
evaporated.  It  is  recommended  that  a specification  insuring  products 
of  a definite  character  should  be  used  and  that  no  road  oils  be  bought 
on  a guarantee  of  a certain  per  cent  of  “asphaltum  base,”  or  of  only  a 
certain  gravity. 

California  was  the  first  state  to  use  oils  extensively  on  earth  roads. 
Fairly  heavy  oils  were  applied  with  some  success,  due  partly  to  the 
sandy  soil  and  fairly  warm  and  dry  climate  of  California.  In  Illinois, 
soil  and  climatic  conditions  make  it  necessary,  however,  to  use  some- 
what 1'ighter  oils.  An  oil  meeting  the  requirements  of  specifications 


Figure  31 . A Sand  Oil  Road  Built  in  Layers  of  Sand  in  Which  Oil  Has  Been  Incorporated . A 
Similar  Construction  Has  Been  Used  on  a Few  Earth  Roads  in  Illinois. 


No.  4 might  be  used  successfully  on  a sandy  soil.  It  is  essential  when 
using  an  oil  of  this  kind  that  the  dust  should  have  been  well  settled  by 
a good  rain  or  repeated  sprinkling,  and  that  the  road  should  be  dry 
and  almost  dustless  at  the  time  of  the  application.  The  light  oils 
obtained  under  specifications  No.  6 are  more  suitable  for  clay  soils 
and  roads  which  are  somewhat  dusty  at  the  time  of  application.  No 
material,  however,  can  be  expected  to  give  satisfaction  on  a road 
which  is  covered  with  a thick  layer  of  dust  or  is  badly  rutted,  and  the 
less  dust  at  the  time  of  application,  the  better  will  be  the  results. 

SPECIFICATIONS  NO.  6. 

LIGHT  OILS  FOR  SURFACE  TREATMENT  OF  EARTH  ROADS. 

(Cold  Application.) 

1.  The  oil  shall  be  a fluid  product  free  from  water. 

2.  Specific  Gravity.  Its  specific  gravity  at  25°  C.  (77°  F.)  shall 
not  be  less  than  0.910. 


36 


3.  Total  Bitumen..  It  shall  be  soluble  in  chemically  pure  cold 
carbon  disulphide  to  the  extent  of  at  least  99.5  per  cent. 

4.  Naptha  Insoluble  Bitumen.  Of  the  total  bitumen  not  less 
than  1.5  shall  be  insoluble  in  86°  B.  paraffin  naphtha  at  air  temperature. 

5.  Fixed  Carbon.  The  fixed  carbon  shall  not  be  less  than  2.5 
per  cent. 

6.  Viscosity.  When  240  cc.  of  the  oil  are  heated  in  an  Engler 
Viscosimeter  to  50°  C.  (122°  F.)  and  maintained  at  this  temperature 
for  five  minutes,  the  first  50cc.  which  flow  through  the  aperture  shall 
show  a specific  viscosity  of  not  less  than  five  nor  more  than  fifteen. 

7.  Loss  on  Evaporation.  When  20  grams  of  the  oil  (in'  a tin 
dish  %y2  inches  in  diameter  and  three-fourths  inch  deep  with  vertical 
sides)  are  maintained  at  a temperature  of  163°  C.  (325°  F.)  for  five 
hours  in  a N.  Y.  Testing  Laboratory  oven,  the  loss  shall  not  exceed 
25  per  cent  by  weight. 

Crude  tars  have  also  been  employed  as  dust  palliatives,  but  on 
account  of  the  injury  they  cause  to  rubber  tires  and  when  tracked  into 
houses,  they  are  not  recommended.  As  a rule,  in  surface  oiling,  the 
heaviest  products  that  can  be  applied  successfully  under  the  given 
conditions  will  give  the  best  results,  and  the  extra  cost  of  paying  1 or 
2 cents  more  per  gallon  to  obtain  a suitable  grade  of  oil,  instead  of  the 
cheapest  grades,  will  be  more  than  offset  by  the  differences  in  the 
results  obtained. 

The  price  of  the  oils  used  on  earth  roads  varies  from  about  3 to  6 
cents  per  gallon.  They  are  applied  at  the  rate  of  one-eighth  to  one- 
third  gallon  per  square  yard,  and  the  average  cost  of  application  is 
about  1 cent  per  gallon.  Precautions  should  be  taken  not  to  add  an 
excess  of  oil,  and  in  general,  a couple  of  light  applications  (of  say 
one-eighth  gallon  per  square  yard)  during  the  year  will  give  better 
results  than  a single  application  of  the  total  amount. 


MISCELLANEOUS  BITUMINOUS  MATERIALS. 

Various  oil  distillates  and  tar  products  other  than  coal  tar  are  at 
present  on  the  market.  Some  mixtures  of  tar  and  asphalt  have  been 
used  with  good  results  within  recent  years.  Water  gas  (oil  gas)  tars, 
although  not  generally  considered  as  good  road  binders,  have  also  been 
used  with  some  success  for  the  surface  treatment  of  roads.  As  a rule, 
the  oil  and  tar  distillates  have  been  of  no  importance  as  dust  pre- 
ventives and  of  no  value  as  binders. 

It  is  practically  impossible,  at  the  present  time,  to  cover  by  specifi- 
cations the  various  mixtures  of  tar  and  asphalt,  which  are  used  either 
as  binders  or  dust  preventives.  Should  it  be  desired  to  use  such 
products,  the  consistency  of  a suitable  mixture  should,  however,  be 
specified ; that  is,  a product  with  a float  test  of  one  and  one-half  to  two 
and  one-half  minutes,  at  32°  C.  might  be  satisfactory  for  a hot  applica- 
tion on  a macadam  road,  while  a lighter  product  having  a specific 
viscosity  of  ten  to  twenty-five  at  50°  C.  would  be  more  suitable  for  a 
dusty  gravel  road. 


OIL  AND  TAR  EMULSIONS. 

These  emulsions  consist  essentially  of  a mixture  of  oil  and  water 
or  tar  with  water,  and  are  used  for  laying  dust.  Oil  and  water  do  not 
mix  under  ordinary  conditions,  but  a mixture  may  be  obtained  by 
mechanical  or  chemical  means. 

Mechanical  emulsions  are  prepared  in  specially  designed  apparatus 
such  as  the  “Emulsifix,”  which  mixes  the  oil  and  water  by  means  of 
rapidly  whirling  wheels.  These  emulsions  are  applied  to  the  road  as 
soon  as  they  are  formed,  as  they  are  very  unstable  and  separate  imme- 
dately  upon  standing. 

Tar,  vegetable  and  animal  oils  can  be  emulsified  with  water  after 
addition  of  a small  amount  of  a saponifying  agent  such  as  potash, 
caustic  soda  or  ammonia.  Petroleum  products  such  as  the  road  oils 
will  not  saponify  directly  with  .alkalies,  and  to  obtain  an  emulsion,  it  is 
necessary  to  add  a small  amount  of  cheap  soap  or  of  saponifying 
materials,  such  as  a combination  of  animal  or  vegetable  fats  and  an 
alkali.  Emulsions  of  this  kind  are  sold  in  concentrated  form,  and  are 
mixed  with  a large  amount  of  water  before  being  applied.  Their 
value  will  vary  a great  deal  with  the  character  of  the  oil.  An  asphaltic 
or  semi-asphaltic  oil  of  good  quality  will  tend  to  bind  the  dust  particles 
and  repeated  applications  will  tend  to  form  a thin  mat  surface,  while 
a greasy  paraffin  oil  may  have  poor  dust-laying  properties,  and  an 
accumulation  of  this  oil  may  form  in  rainy  weather  a slippery  mud 
very  undesirable  for  traffic.  • 

Many  methods  have  been  used  in  preparing  these  emulsions,  and 
it  is  impossible  to  describe  them  in  this  bulletin.  The  following  prep- 
arations, which  have  been  used  in  the  parks  of  Boston  and  Chicago, 
and  which  are  described  by  Hubbard  in  “Dust  Preventives  and  Road 
Binders,”  may  be  taken  as  illustrations  of  the  methods  and  materials 
used.  In  Boston,  10  to  15  pounds  of  cotton  seed  oil  soap  are  first 
dissolved  in  50  gallons  of  water  by  the  aid  of  steam  heat.  To  every 
50  gallons  of  soap  solution,  100  gallons  of  semi-asphaltic  oil  are  added 
and  emulsified  through  agitation  by  a steam  pump.  This  forms  a stock 
solution  containing  66  per  cent  of  petroleum,  which  is  further  diluted 
with  water  before  application. 

In  Lincoln  Park,  Chicago,  a mixture  of  Kansas  and  California 
oils  is  emulsified.  In  this  case,  a naptha  soap  is  employed  because  it  is 
found  to  work  best  with  the  hard  lake  water.  Fifteen  pounds  of  the 
soap  are  dissolved  in  60  gallons  of  hot  water,  and  60  gallons  of  Kansas 
oil  are  added.  A system  of  hogsheads  and  pipes  permits  agitation  by 
means  of  a steam  pump.  After  a few  minutes,  one-half  barrel  of 
California  asphaltum  is  added  and  the  whole  mixture  is  emulsified  for 
about  20  minutes  longer.  The  emulsion  is  then  made  up  to  800  gallons 
with  boiling  water  and  applied  with  an  ordinary  sprinkler. 

For  a first  application  an  emulsion  should  contain  from  10  to  15 
per  cent  of  oil,  while  a smaller  per  cent  may  be  used  for  repeated 
treatments. 

Oil  emulsions  have  been  applied  mainly  on  parkways,  and  to  some 
extent  on  suburban  roads.  Up  to  the  present  time,  they  have  not  been 
used  to  any  extent  on  rural  roads,  due  mainly  to  the  necessity  of 
repeated  treatments. 


38 


CALCIUM  CHLORIDE. 

Calcium  chloride  is  a salt,  which  owes  its  use  as  a dust  preventive 
to  its  hygroscopic  properties  and  its  cheapness.  The  fact  that  it  is 
clean  and  odorless  has  contributed  also,  somewhat,  to  make  it  popular 
in  many  cities. 

It  is  obtained  mainly  as  a by-product  in  the  manufacture  of  com- 
mon washing  soda  by  the  Solvay  process.  As  the  use  of  calcium 
chloride  for  purposes  other  than  dust-laying  is  relatively  small,  it  can 
be  obtained  fairly  cheap. 

It  absorbs  moisture  very  readily,  and  in  moist  air  will  take  up 
about  twice  its  weight  of  water.  It  crystallizes  with  almost  its  own 
weight  of  water,  but  when  heated  to  about  85°  F.  these  crystals  will 
melt,  and  at  the  highest  temperatures  on  a road  surface  about  one-third 
of  the  water  which  it  requires  for  crystallization  is  available  before  it 
becomes  solid.  It  tends,  therefore,  to  retain  moisture  for  a consider- 
able length  of  time  after  an  ordinary  application  of  water  would  have 
evaporated. 

Calcium  chloride  is  sold  either  in  solution  or  in  a solid,  fused  or 
granular  condition.  The  solid  material  contains  about  75  per  cent 
calcium  chloride  and  25  per  cent  moisture,  and  at  the  present  time, 
can  be  purchased  at  $13.00  to  $16.00  per  ton  or  $2.45  to  $3.00  per 
drum  f.  o.  b.  at  points  of  manufacture.  In  solution  it  is  usually  sold 
in  a concentrated  form,  containing  about  40  per  cent  calcium  chloride, 
and  having  a specific  gravity  of  1.40  or  41— |— 0 B.  at  ordinary  temper- 
ature. 

Calcium  chloride  is  applied  either  dry  or  in  solution.  In  the  dry 
method,  the  granulated  material  is  spread  over  the  road  at  a rate  of 
about  1 pound  per  square  yard.  As  a rule,  the  calcium  chloride  soon 
absorbs  enough  moisture  from  the  air  to  dissolve,  but  in  hot  dry 
weather  it  is  necessary  to  follow  the  application  by  a light  sprinkling 
with  water.  Solutions  containing  about  15  to  20  per  cent  of  calcium 
chloride,  or  about  1)4  to  2 pounds  of  the  solid  product  per  gallon  of 
water,  are  applied  at  the  rate  of  0.3  to  0.5  gallons  per  square  yard  from 
ordinary  sprinkling  tanks.  These  applications  must  be  followed  from 
time  to  time  by  lighter  treatments  of  about  one-half  these  quantities, 
and  in  very  dry  weather  with  occasional  sprinklings  with  water.  The 
value  of  an  application  of  calcium  chloride,  and  the  length  of  time 
during  which  it  will  be  efficient  will  vary  a great  deal  with  weather 
conditions  and  with  local  conditions,  from  a few  days  to  a few  months. 
It  is  best  suited  for  use  in  residence  districts  where  the  traffic  is  rather 
light  and  where  a water  supply  is  convenient,  but  should  always  be 
applied  while  the  road  is  practically  dustless.  It  is  also  very  efficient 
for  the  temporary  treatment  of  dust  on  race  tracks,  fair  grounds,  etc., 
but  is  not  generally  considered  satisfactory  for  rural  roads  on  account 
of  the  necessity  of  convenient  water  supply  and  repeated  treatments. 

Commercial  calcium  chloride  may  be  obtained  in  an  almost  pure 
condition,  and  the  amount  of  calcium  chloride  in  a solution  of  such  a 
product  may  be  found  almost  directly  by  reading  its  specific  gravity 
or  degree  Beaume  with  a hydrometer.  The  following  table  gives  a 


39 


comparison  of  these  readings,  together  with  the  calcium  chloride  con- 
tent of  the  solution : 

Per  cent  calcium  chloride 5 10  15  20  30  40 

Specific  gravity  at  25°  C.  (77°  F.) . . . .1.04  1.08  1.13  1.18  1.28  1.40 

Degrees  Beaume  at  25°  C.  (77°  F.) . . . 6 11  17  22  32  41-j- 

The  above  tables  do  not  apply,  however,  when  the  solution  con- 
tains noticeable  amounts  of  impurities  and  an  analysis  of  the  solution 
becomes  necessary.  Calcium  and  magnesium  hydrates,  and  sodium 
and  magnesium  chlorides  are  the  usual  impurities.  Magnesium 
chloride  has  good  dust-laying  qualities,  but  the  other  salts  have 
little  or  no  value  in  dust  prevention. 

MISCELLANEOUS  MATERIALS. 

A number  of  miscellaneous  materials  have  been  used  either  for 
dust  laying  or  for  the  construction  of  more  or  less  dustless  roads. 
Only  two  of  these  products,  “glutrin”  and  “road  silicate,”  will  be 
considered  in  this  chapter.  Both  have  been  used  to  a small  extent  in 
this  State. 

Glutrin  is  a concentrated  residue  of  the  waste  sulphite  liquor 
which  is  obtained  as  a by-product  in  the  manufacture  of  wood  pulp 
by  the  sulphite  process.  The  crude  liquor  has  little  or  no  binding 
value,  but  when  concentrated  to  about  one-fifth  of  its  volume  to  a 
specific  gravity  of  about  1.25,  it  becomes  somewhat  sticky  and  exhibits 
fairly  good  binding  qualities.  It  is  applied  diluted  with  its  own  volume 
of  water  at  the  rate  of  about  one-half  gallon  per  square  yard.  Its 
manufacturers  claim  that  its  value  as  a binder  is  due  not  only  to  its 
stickiness,  but  also  to  the  fact  that  a chemical  action  takes  place  be- 
tween the  glutrin  and  the  stone,  resulting  in  a better  bond  of  the  road 
surface.  As  glutrin  is,  however,  soluble  in  water,  it  will  be  washed 
out  by  frequent  rain,  and  to  prevent  this;  its  application  is  often  fol- 
lowed by  surface  oiling  to  waterproof  the  road. 

Its  cost  at  the  present  time  is  about  15  cents  per  gallon  at  points 
of  manufacture,  and  its  application  seems  to  be  limited  to  macadam 
and  gravel  roads. 

Solutions  of  sodium  silicate,  or  water  glass,  have  been  used  to 
some  extent  as  dust  preventives  and  road  binders.  A product  is  now 
on  the  market  under  the  name  of  “road  silicate,”  which  contains 
about  40  per  cent  of  almost  pure  sodium  silicate.  Its  specific  gravity 
is  approximately  1.40,  and  it  is  sold  at  about  $15  per  ton.  When 
applied  to  a macadam  or  gravel  road,  it  will  tend  to  bind  the  stone 
cither  by  leaving  a film  of  water  glass  between  the  stone,  or  with  basic 
stone  such  as  limestone,  by  forming  some  insoluble  silicates.  As  ordi- 
narily applied,  however,  in  rather  weak  solutions,  it  is  not  present  in 
sufficient  quantities  to  form  a strong  bond,  and  the  thin  cementing 
films  which  are  formed  are  likely  to  break  under  traffic.  On  account 
of  its  high  cost  it  is  doubtful,  however,  if  enough  sodium  silicate  can 
be  added  to  give  a satisfactory  road  without  making  the  cost  of  con- 
struction prohibitive. 


40 


SUITABILITY  OF  MATERIALS. 

It  has  been  seen  from  the  foregoing  discussion  that  the  success  in 
the  building  of  dustless  roads  will  depend  mainly  upon  two  factors : 

1.  Proper  construction  when  conditions  of  weather  and  (in  sur- 
face treatment)  conditions  of  the  road  are  suitable. 

2.  Suitable  materials. 

Proper  construction  is  to  a large  extent  a question  of  experience. 
It  is  recommended,  however,  that  in  all  surface  treatments  with  oils 
and  miscellaneous  dust  preventives,  all  materials  be  applied  when  the 
road  is  in  a practically  dustless  condition  after  all  ruts  and  depressions 
have  been  eliminated,  and  that  the  road  (also  the  stone  and  sand)  be 
dry  when  bituminous  materials  are  applied. 

Suitable  materials  are  here  understood  to  mean,  not  only  good 
materials,  but  the  materials  which  are  best  suited  for  the  individual 
conditions  of  each  road.  Enough  emphasis  cannot  be  placed  upon  the 
fact  that  even  a very  good  product  may  not  be  desirable  for  a certain 
work.  Many  factors  are  to  be  taken  into  consideration  in  the  selection 
of  a bituminous  material  or  other  dust  preventives,  and  chief 
among  them,  the  type  of  road,  the  condition  of  the  surface,  the  char- 
acter of  traffic,  the  requirements  of  the  public  and  the  amount  of 
money  available.  After  a product  has  been  decided  upon,  it  should 
be  purchased  under  a well  written  set  of  specifications  which  will 
eliminate  all  undesirable  materials.  An  attempt  has  been  made  in  this 
bulletin  to  give  a number  of  specifications  for  bituminous  products  in 
connection  with  various  types  and  conditions  of  road  surfaces.  It 
should  be  remembered,  however,  that  the  specifications  are  given 
merely  as  a guide,  and  that,  while  the  materials  which  meet  their 
requirements  will  be  suitable  in  most  cases,  yet  peculiar  conditions 
may  arise  for  which  they  are’ not  satisfactory.  Good  judgment  in  the 
selection  of  materials  requires  a great  deal  of  experience  as  to  their 
qualities  and  character.  As  few  of  the  township  and  city  officials  are 
usually  in  position  to  acquire  this  experience,  the  State  Highway  De- 
partment stands  ready  to  assist  them  in  securing  the  desired  informa- 
tion. Its  testing  department  is  equipped  to  make  the  tests  of  all  road 
materials,  and  it  will  furnish  advice  to  road  officials  free  of  charge. 
It  is  urged,  however,  that  all  available  information  in  regard  to  condi- 
tions of  road  and  traffic  be  given  when  requests  for  testing  of  materials 
are  made.  This  information  will  save  time  and  will  often  contribute 
a great  deal  towards  the  success  of  the  construction. 


